| Document and Entity Information | Jun. 30, 2023 | May 10, 2023 |
| Cover [Abstract] | ||
| Amendment Flag | false | |
| Entity Central Index Key | 0001662244 | |
| Document Type | 8-K | |
| Document Period End Date | Jun. 30, 2023 | |
| Entity Registrant Name | Cyteir Therapeutics, Inc. | |
| Entity Incorporation State Country Code | DE | |
| Securities Act File Number | 001-40499 | |
| Entity Tax Identification Number | 45-5429901 | |
| Entity Address, Address Line One | 99 Hayden Ave, Building B | |
| Entity Address, Address Line Two | Suite 450 | |
| Entity Address, City or Town | Lexington | |
| Entity Address, State or Province | MA | |
| Entity Address, Postal Zip Code | 02421 | |
| City Area Code | 857 | |
| Local Phone Number | 285-4140 | |
| Written Communications | false | |
| Pre Commencement Tender Offer | false | |
| Pre Commencement Issuer Tender Offer | false | |
| Security 12b Title | Common Stock, $0.001 par value per share | |
| Trading Symbol | CYT | |
| Security Exchange Name | NASDAQ | |
| Entity Emerging Growth Company | true | |
| Entity Ex Transition Period | false |
